ASPECTS OF THE BIOLOGY AND ECOLOGY OF THE COCONUT CRAB BIRGUS LATRO (LINNAEUS, 1767) ON ISLANDS WITHIN THE KISITE-MPUNGUTI MARINE PROTECTED AREA, KENYA
Wato, Jillo Katello
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The Coconut crab Birgus latro (Linnaeus, 1767) is widely distributed on remote tropical islands of the Pacific and Indian Oceans. Populations of B. latro are declining throughout their range, with loss of habitat and harvesting for human consumption thought to be key drivers of the decline. The species is considered data-deficient under the IUCN Red-List. In East Africa, the population of B. latro is poorly studied and thus little is known about their status. Although published data indicates that the western limit of the species range is Chumbe Island in Zanzibar, a population of B. latro has been reported on some islands of the Kisite-Mpunguti Marine Protected Area (KMMPA) in Kenya. This study was designed as a baseline investigation of the biology and ecology of the B. latro population within the KMMPA in Kenya. The study was conducted during February - June 2016 on the Mpunguti Lower East (4.5 ha) and West (5 ha) Islands within the MPA. These Islands are often referred to simply as Mpunguti East (MPE) and Mpunguti West (MPW). A combination of the Leslie catch-depletion method, mark-recapture and plot techniques were used to study the population (size-sex structure, morphometric characteristics, abundance and density) of B. latro in the two Islands of Mpunguti. A total of 304 specimens (excluding recaptures) were sampled on the two Islands during the study period: 52.3% of specimens from Mpunguti Lower West Island while 47.7% were from Mpunguti Lower East Island. Analysis of abundance showed a population density of 82.8 inds. /ha for Mpunguti Lower West and 100.6 inds. /ha for the Mpunguti Lower East Island. The mean Catch per Unit Effort (CPUE) in both Islands was 1.4 ± 0.3 crabs / bait. The highest average CPUE values of 1.8 ± 0.3 and 1.6 ± 0.3 per bait were recorded for Mpunguti Lower East in April and Mpunguti Lower West Island in February, respectively. Results of 2-way ANOVA (after normality test) indicated no variation (F (23.052), p = 0.083155) for the number of crabs caught among plots of Mpunguti Lower vi West and East Islands. However, Mpunguti Lower West plots (MPW-1, MPW-2 and MPW-3) showed homogeneity within plots‘ captures but significant difference among plots‘ population means (df =2, p < 0.05). Mpunguti Lower East plots (MPE-1, MPE-2 and MPE-3) similarly showed homogeneity within plots captures but no significant difference among plots‘ population mean (df = 2, p = 0.6181). Different morphometric characters in males and females were determined from 139 males and 165 females used for these analyses. Significant (p<0.05) positive linear relationships between different body dimensions of the B. latro were observed. No significant difference (χ2 = 2.386, df = 1, p = 0.122) was observed between male and female sex ratio (1:1.2). Analysis of sex morphometric data indicated that the associated size-frequency distributions were significantly different (p< 0.05) with males reaching a larger size than females, demonstrating a pronounced sexual size dimorphism in B. latro. This study presents vital information and documents Kenya as part of the range of this species.